Libra

Libra


Transit Date of principal star:
5 May


Libra means "The Scales" or "Balance", so named because when the zodiac was still in its infancy, some four thousand years ago, the sun passed through this constellation at the autumnal equinox (21 September). At the two equinoxes (Spring and Autumn) the hours of daylight and darkness are equal.

As a symbol for equality, the constellation came to represent Justice in several middle Eastern cultures. However, the Greeks had a different perspective; at one time Scorpius, which lies just to the east, was much larger, and the stars that make up Libra were then known as the Claws of the Scorpion.

Eventually, however, these stars of Libra came to represent the Golden Chariot of Pluto. The story of Pluto's abduction of Persephone is a widely known Greek myth, perhaps because it has such a strong astronomical association.

Pluto's (or Hades') Golden Chariot was used whenever the Lord of the Underworld wished to visit the Upperworld, usually to seduce a nymph. But when he took Persephone back to Tartarus, the deepest part of Hades, the Upperworld would change forever.

The name of the ruler of the Underworld was actually Hades. Hades was a brother of Zeus and of Poseidon; he was usually ignorant of the happenings of the Upperworld, only emerging rarely from his dark kingdom.

Deep beneath the earth, he owned all its mineral riches, but his favourite possession was a gift from the Cyclopes: a helmet that rendered him invisible. (Those familiar with Wagner's Ring Cycle will recognise the leitmotif, and a number of others in this story of Persephone.)

It was considered imprudent and dangerous to mention the names of certain gods and goddesses. Thus the Furies, or Cronies, were called Eumenides (Kindly Ones), and Hades was called Pluto (Rich One).

His golden chariot was pulled by four jet-black horses. While he used the chariot to periodically visit the Upperworld, in order to seduce a beautiful nymph, he rarely wished the relationship to last. Until he saw Persephone, the daughter of Demeter and Zeus.

Demeter was the sister of Zeus and Hades, and one of the most important of goddesses as she was responsible for Agriculture, and all growing things.

Hades is so enamoured by the beauty of Persephone, he wants her for his own, so takes her by force down to his kingdom, where she becomes the Queen of the Underworld.

Demeter mourns for her lost daughter and begs the other gods for help. So Theseus and Peiritheus (his brother) descend into Hades in search of Persephone, but are unsuccessful. In fact, they are held captive by Hades, and Heracles is sent to rescue them. He can only manage to bring back Theseus; Peiritheus is condemned to remain forever in Hades.

Demeter is so distraught about the loss of her daughter she decides to forbid any seeds from sprouting. A vast drought spreads throughout the Upperworld. Zeus becomes vexed, for he is owed a certain tribute, and if the drought continues his tribute will not be forthcoming.

Some accounts give Zeus a more noble reason for acting on his sister's behalf: that he empathizes with Demeter and wishes to rectify her loss. In any event, he convinces his brother Hades to give up Persephone, so that the Upperworld can again become green and lush.

Hades agrees, provides that Persephone hasn't eaten anything since her arrival. Alas, she had consumed six pomegranate seeds, so Hades claims she cannot return.

Zeus will have none of it, and rules that she must forever divide her time between the Upperworld and the Underworld; four months out of the year she must stay with her husband, while the rest of the year she may visit her mother, in the Upperworld.

Thus every year the world retreats briefly into a cold and forbidding place, until the 21st of March, when Persephone is allowed to emerge from the Underworld, bringing Spring with her.


The Bayer stars are fairly dim, except for two two-magnitude stars, alpha2 and beta. The constellation has several objects of interest, including some fine double stars and an unusual variable.

Alpha Librae is also known as Zubenelgenubi, a derivation of an older Arabic name that translates into "Southern Claw" (i.e. of the Scorpion). The star is a wide binary of unequal stars (see below).

Beta Librae is called Zubeneschamali, "The Northern Claw". This white star has been described by some to be green in colour; Burnham points out that truly green stars are close companions to red stars (such as the companion to Antares), and beta Librae doesn't fit that category. Still, the impression apparently persists for some observers; you'll have to decide for yourself.


Double stars in Libra:

Alpha2 and alpha1 Librae form a very wide double with colour contrast: yellow and pale blue. Note that alpha2 is the primary: 2.7, 5.2; PA 314, separation 231.1".

Iota Librae is a multiple system:

The companion iota1a is a rapid binary with a period of 22.35 years, travelling in a retrograde motion.

Iota1B is a fixed wide companion: 4.5, 10.9; PA 110, separation 57".

Struve 1962 is a fixed pair of equal stars: 6.4, 6.5; PA 188, separation 11.9".


Variable stars in Libra:

Delta Librae is an Algol-type variable: 4.9-5.9 with a period of 2.3 days.

48 Librae (also known as FX Librae) is a noted shell star that may be dormant for many years, then show rapid activity.

The star has an exceptionally large rotational velocity, and (perhaps as a consequence) an equatorial ring of gases about twice the diameter of the star which rapidly expands.


Deep Sky Objects in Libra:

The only notable deep sky object is a rather loose globular cluster of faint stars: NGC 5897, thought to be about 50,000 light years away. The larger the telescope, the better the impression.

The cluster is found two degrees southeast of iota Librae.


For a more detailed appreciation of Libra, visit the Binocular Section.


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